Janette Mercer had backed up her son 'with more lies' during the investigation into the killing of Rhys Jones, the judges said. Photograph: Martin Rickett/PA

The mother of the teenage gunman who murdered Rhys Jones lost an appeal today against her three-year jail sentence for perverting the course of justice.

Three judges at the court of appeal in London ruled that the sentence imposed on Janette Mercer at Liverpool crown court in April was not "manifestly excessive".

Mercer, 49, who admitted the charge, supported her son Sean when he told police he owned a black and cream mountain bike, not the silver bicycle that was caught on CCTV in use by the gunman.

Rejecting her application for permission to appeal, Mr Justice Blair said she had known that her son was a key suspect, the importance of the silver bike and that her son had told lies about it. He said she had "backed him up with more lies".